Armored flat cable signalling and instrument power acquisition

ABSTRACT

Measurement and/or control units located within a borehole are inductively coupled to a flat three phase power cable segment without piercing the armor around the cable. For drawing power from the cable, C-shaped, L-shaped or straight core(s) with winding(s) around at least a portion thereof are positioned proximate to one or both end conductors, outside the armor, with significantly overlapping the center conductor. For impressing or detecting signals on the cable, straight core(s) with winding(s) around at least a portion thereof are disposed on one or both sides of the cable, outside the armor, across all three conductors with the core oriented transverse to the cable conductors.

TECHNICAL FIELD OF THE INVENTION

The present invention is directed, in general, to borehole production signaling and power systems and, more specifically, to impressing signals on and drawing power from borehole production power cables without intrusive connection.

BACKGROUND OF THE INVENTION

In borehole production systems that employ artificial lift equipment such as electrical submersible pumps (ESPs), a three phase power cable transmits power downhole to the motor and pump. In addition, various schemes have been proposed for transmitting data measurement and control signals over the three phase power cable, including transmission of such data measurement and control signals concurrently with the three phase power.

Current systems for transmitting measurement and control signals over the power cable and/or powering downhole electronics from the three phase power to the pump motor typically require direct connection to the cable conductors. Such direct connection requires piercing the cable armor, creating a point at which the cable might become susceptible to attack by hostile conditions downhole.

There is, therefore, a need in the art for indirectly coupling to power cable conductors, without piercing the cable armor, in order to draw power or transmit signals.

SUMMARY OF THE INVENTION

To address the above-discussed deficiencies of the prior art, it is a primary object of the present invention to provide, for use in a borehole production system, measurement and/or control units located within a borehole that are inductively coupled to a flat three phase power cable segment without piercing the armor around the cable. For drawing power from the cable, C-shaped, L-shaped or straight core(s) with winding(s) around at least a portion thereof are positioned proximate to one or both end conductors, outside the armor, with significantly overlapping the center conductor. For impressing or detecting signals on the cable, straight core(s) with winding(s) around at least a portion thereof are disposed on one or both sides of the cable, outside the armor, across all three conductors with the core oriented transverse to the cable conductors.

The foregoing has outlined rather broadly the features and technical advantages of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art will appreciate that they may readily use the conception and the specific embodiment disclosed as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. Those skilled in the art will also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.

Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, it may be advantageous to set forth definitions of certain words or phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, whether such a device is implemented in hardware, firmware, software or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, and those of ordinary skill in the art will understand that such definitions apply in many, if not most, instances to prior as well as future uses of such defined words and phrases.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, wherein like numbers designate like objects, and in which:

FIG. 1 depicts a borehole production system including downhole measurement and/or control units inductively coupled to a flat three phase power cable according to one embodiment of the present invention;

FIGS. 2A through 2D are diagrams of configurations for inductive coupling of downhole signaling units to a flat three phase power cable according to various embodiments of the present invention; and

FIG. 3 depicts positioning of an inductive coupling device relative to a flat portion of a power cable within production tubing according to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 through 3, discussed below, and the various embodiments used to describe the principles of the present invention in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the invention. Those skilled in the art will understand that the principles of the present invention may be implemented in any suitably arranged device.

FIG. 1 depicts a borehole production system including downhole measurement and/or control units inductively coupled to a three phase power cable according to one embodiment of the present invention. Borehole production system 100 includes an electrical submersible pump and motor assembly 101 lowered into a borehole 102 using a production tubing string 103. A three-phase power cable 104 carries three-phase power into the borehole 102 to the motor within assembly 101 from a surface location.

At the surface, a three-phase power source 105, such as a generator or a connection to a local power grid, is coupled to power cable 104 by a converter/inverter system 106. Converter/inverter system 106 is constructed and operates in a manner known in the art to operate and/or regulate the operating speed of the motor/pump assembly.

Those skilled in the art will recognize that the complete structure and operation of a borehole production system is not depicted in the drawings or described herein. Instead, for simplicity or clarity, only so much of the borehole production system as is unique to the present invention or necessary for an understanding of the present invention is depicted and described.

At least a portion of three phase power cable 104 is flat. In fact, generally only a portion of the three phase power cable 104—the “motor lead” piece transmitting power around the pump within the production string—will be flat. The conductors for each phase within any three phase power transmission cable, flat or round, are generally in relatively close proximity. In round cables, each conductor, as seen from a cross-section, is spaced an equal distance from the other two at the apex of an equilateral triangle. As a result, the variations in external magnetic fields produced by instantaneous currents (or the differential magnetic field resulting from individual currents) may not be of sufficient magnitude to draw power by inductive coupling.

However in flat three phase cables or cable segments, the conductors, as seen from a cross-section, all lie within a common plane. The distance between each end conductor and the remaining two conductors (the center conductor and the other end conductor) is different. Currents within the other two conductors therefore have disparate inductive effects on the end conductors. Due to the significant separation in influence from the other two conductors, variations in the total magnetic field accessible near an end conductor is intensified, making access to power by inductive coupling viable.

In many applications, such as downhole motor applications where casing and tubing dimensions do not leave enough room for round cable, use of flat cable is imperative, or at least highly desirable. In addition to dimensional considerations, logistics or splicing concerns may drive the use of flat cable. Even where round cable is employed for power transmission, in ESP systems a “motor lead” piece of flat cable is normally spliced to the round cable above the pump to run power past the pump to the motor. Thus at least a section of flat cable is typically available in the three phase power transmission system for an ESP.

In the present invention, at least a portion of three phase power cable 104 is flat. Alternatively, the entire three phase power cable 104 may be a flat cable, connected to a system inductance balancer 107 of the type described in U.S. Pat. No. 6,566,769.

A number of data measurement or control signaling units 108 a-108 n, which may be transmitters, receivers, or transceivers (hereinafter collectively referred to as “signaling units”), are optionally positioned proximate to power cable 104 at various locations along the length of that cable. Signaling units 108 a-108 n may be located, for example, at the surface, at the wellhead (particularly for subsea wells), at or near a packer, at various intervals within the well, and/or at the top of the motor/pump assembly. Signaling units 108 a-108 n are constructed, disposed and oriented relative to the conductors of cable 104, of flat segments of cable 104, as described in further detail below. At a minimum, at least one signaling unit 108 n having such construction, disposition and orientation is positioned proximate to a motor lead segment of cable 104 or another flat portion of cable 104.

In addition, a data logging and/or control surface system 109 is coupled to one or more conductors of power cable 104, for receiving or transmitting signals to measurement and/or control units 108 a-108 n. Signaling units 108 a-108 n may measure pressure, temperature, cut, flow rate, or other parameters, and/or may control valves or other downhole mechanical systems. Signaling units 108 a-108 n may be configured to communicate bi-directionally with surface system 109, either alone (one at a time) or concurrently, and may transmit or receive signals over three phase cable 104 concurrently with the three phase power transmitted to drive motor/pump assembly 101. Based on measurements returned by signaling units 108 a-108 n to surface system 109, surface system 109 controls operation of the production system, including varying the speed of the motor, opening and closing valves, etc.

In the present invention, signaling units 108 a-108 n are inductively coupled to the conductors of a flat segment within power cable 104 for the purposes of (a) transmitting or receiving signals over such conductors, and/or (b) drawing power from three phase power cable 104 as described in further detail below. As known in the art, filters may be required within signaling units 108 a-108 n and surface system 109 to filter the three phase power transmitted over power cable 104 concurrently with data measurement or control signals.

FIGS. 2A through 2D are diagrams of configurations for inductive coupling of a signaling unit to conductors for a flat three phase power cable segment according to various embodiments of the present invention. To avoid having to pierce the cable armor for three phase cable 104, at least one signaling unit 108 n is inductively coupled to the three phase cable 104, physically accessing the magnetic field produced by current carried on the conductor to inductively receive power from three phase cable 104, and impressing signals upon or detecting signals from three phase cable 104 by similar use of a magnetic field producing current(s) within the conductor(s). Different configurations of the inductive coupling mechanism, and different positions relative to the conductors of the three phase power cable 104, are better suited to receiving power and signaling.

FIG. 2A is a diagram for the structure and orientation of an inductive coupling device 200 for inductively coupling signaling unit 108 n to a flat segment within three phase cable 104 for the purpose of drawing power from the three phase power transmitted on the cable 104. Flat cable 104 (or a flat segment within cable 104) includes conductors 201-203 aligned in a plane, with conductors 201 and 203 on the ends and conductor 202 in the center. Each conductor 201-203 is surrounded by insulation 204, with the three conductors 201-203 and the insulation surrounded by armor 205.

For receiving power from cable 104, a inductive coupling device 200 including a generally C-shaped core with a winding around at least a portion thereof is disposed around one of the end conductors 201 or 203. The core is preferable magnetic and/or has a high magnetic permeability.

The strength of the magnetic field created by three phase power transmitted on cable 104 shows greater magnitude or variance on end conductors 201 or 203 than on center conductor 202, or on any conductors within a round three phase cable. This allows physical access to the magnetic field produced by the current on that end conductor—for instance, conductor 201—with a significant separation from the influence of the current carried on the other conductors 202 and 203. The separation of influence from the other conductors 202-203 intensifies the total magnetic field variations proximate to the conductor 201 and thus enhances the amount of power that is accessible.

The C-shape of the core is sized to substantially surround the conductor 202 or 203, preferably without significantly overlapping center conductor 202. The winding may cover substantially all of the core or only a portion thereof. Counterpart inductive coupling devices 200 within a given signaling device 108 n may be disposed around both end conductors 201 and 203. The electrical current produced by the inductive coupling device 200 may be rectified, transformed and/or changed in frequency by electronics (not shown) for use within other functional components in signaling unit 108 n.

FIGS. 2B and 2C are alternative configurations an inductive coupling device for inductively coupling signaling unit 108 n to a flat segment of three phase cable 104 for the purpose of drawing power from the three phase power transmitted on the cable 104. Rather than a C-shaped core and/or winding surrounding the end conductor 203 on three sides, an L-shaped core and/or winding 206 as illustrated in FIG. 2B or a straight core and/or winding 207 as illustrated in FIG. 2C may be employed. As long as the core and/or winding do not extend significantly beyond an end conductor to overlap a portion of a center conductor, any configuration providing physical access to the magnetic field produced by current within an end conductor may be employed. Those skilled in the art will recognize that accessing only the magnetic field produced by current in one conductor is not feasible for a three conductor cable carrying three phase power, but that magnetic effects from other conductors become negligible the further the core is space from that conductor.

It should be noted that the C-shaped and L-shaped cores may optionally be continuously curved to, for example, follow the exterior contour of the armor, rather than being formed from straight segments. The terms “C-shaped” and “L-shaped” are intended generally to differentiate between a core disposed proximate to three or two orthogonal “sides”, respectively, of an end conductor (e.g., surrounding a periphery encompassing an angle of approximately either 270° or 180°), without strictly limiting acceptable geometric shapes. Thus, for example, the inductive device may be implemented by a semi-circular toroid. Similarly, a “straight” core may be implemented with different geometric shapes having a portion disposed proximate to only one “side” of an end conductor. In all case, the winding need not be around the portion of the core that is closest to the end conductor, but may be spaced apart from the end conductor.

FIG. 2D is a diagram of the structure and orientation of an inductive coupling device for inductively coupling signaling unit 108 n to a flat segment of three phase cable 104 for the purpose of impressing signals on and/or detecting signals from the flat cable 104 or a flat segment within cable 104. Inductive coupling device 208 includes a generally straight (e.g., cylindrical, or elongate with a square or rectangular cross-section) core with a winding around at least a portion thereof, and is disposed substantially parallel to the plane containing the conductors 201-203, oriented transverse (across) the conductors 210-203. As with the other inductive devices 200, 206 and 207, the winding need not be around the portion of the core closest to the conductors within the cable.

Data and/or control signals are preferably impressed on all three conductors, as a single transmission medium, by either surface system 109 or any of signaling units 108 a-108 n. Accordingly, the core is preferably sized to a length substantially equal to at least a distance across all conductors 201-203. The winding may cover substantially all of the core or only a portion thereof. Similar to inductive coupling devices 200, 206 and 207, counterpart inductive coupling devices may be disposed on both sides of conductors 201-203 within a given signaling unit 108 n. The electrical signal received from or driven through the inductive coupling device 208 may be filtered, transformed and/or amplified as necessary within signaling unit 108 n.

Each signaling unit 108 a-108 n may include both inductive coupling device(s) 200/206/207 and inductive coupling device(s) 208, appropriately connected to different portions of electronics (not shown) therein and disposed proximate to different flat segments of cable 104. When both devices 200/206/207 and 208 are employed within a given unit 108 a-108 n, the devices 200/206/207 and 208 should be sufficiently spaced to avoid interference.

In addition, each unit 108 a-108 n may include a number of either device(s) 200/206/207, device(s) 208, or both, the respective devices of a given type (for drawing power or impressing/detecting signals) operating in parallel to increase the amount of power drawn or to improve signal impression or detection.

FIG. 3 depicts positioning of an inductive coupling device relative to a flat portion of a power cable along a production tubing string according to one embodiment of the present invention. In the example shown, a pressure vessel 300 is secured to production tubing 301 by a clamp 302. Within a wall of pressure vessel 300 adapted to contact tubing 301, a channel is provided for a segment of flat three phase power cable. Inductive coupling devices 207 (in the example shown) are positioned relative to the end conductors within flat portion of cable 104 as described above, held in position by brackets (not shown) and electrically connected by wiring (also not shown) to electronics on circuit board 303 within the vessel 300.

The present invention allows effective coupling to a flat segment of a three phase power cable without piercing the cable armor and creating a point of potential failure. Power may be drawn from the cable and signals transmitted by inductive coupling to the power cable, using coupling device configured to take advantage of the cable cycle inductance variation in the manner best suited to the desired goal of either drawing power or transmitting signals.

Although the present invention has been described in detail, those skilled in the art will understand that various changes, substitutions, variations, enhancements, nuances, gradations, lesser forms, alterations, revisions, improvements and knock-offs of the invention disclosed herein may be made without departing from the spirit and scope of the invention in its broadest form. 

1. An inductive coupling device comprising: a core having a shape sized to fit around at least a portion of a periphery for an end conductor within a flat three phase power cable segment, outside armor for the cable, without significantly overlapping a periphery for a center conductor within the cable; and a winding around at least a portion of the core, the winding inductively drawing power from three phase power transmitted on the cable when the inductive coupling device is positioned proximate to the end conductor and the cable segment carries three phase power.
 2. The inductive coupling device according to claim 1, further comprising: an other core sized to fit around at least a portion of a periphery for another end conductor within the flat three phase power cable segment, outside armor for the cable segment, without significantly overlapping the periphery for the center conductor within the cable segment; and a winding around at least a portion of the other core.
 3. The inductive coupling device according to claim 1, wherein the core has a C-shape, an L-shape, or is straight.
 4. The inductive coupling device according to claim 1, further comprising: a straight core disposed proximate the cable segment outside the armor, the straight core oriented transverse to conductors within the cable segment and having a length substantially spanning a width across the conductors; and a winding around at least a portion of the straight core and inductively impressing or detecting signals on the cable segment.
 5. A borehole production system including the inductive coupling device according to claim 1, the borehole production system further comprising: a three phase power cable including the cable segment, wherein the cable electrically connects artificial lift equipment within a borehole to a surface system; one or more measurement and/or control units coupled to the cable by the inductive coupling device.
 6. An inductive coupling device comprising: a straight core disposed proximate a flat three phase power cable segment on one side of the cable segment and outside armor for the cable segment, the straight core oriented transverse to conductors within the cable segment; and a winding around at least a portion of the straight core and inductively impressing or detecting signals on the cable segment.
 7. The inductive coupling device according to claim 6, further comprising: an other straight core disposed proximate the cable segment on an opposite side of the cable segment and outside armor for the cable segment, the straight core oriented transverse to conductors within the cable segment; and a winding around at least a portion of the other straight core.
 8. The inductive coupling device according to claim 6, further comprising: a C-shaped core sized to fit around an end conductor within the cable segment, the C-shaped core disposed outside armor for the cable segment; a winding around at least a portion of the C-shaped core, the winding inductively drawing power from three phase power transmitted on the cable segment.
 9. A borehole production system including the inductive coupling device according to claim 6, the borehole production system further comprising: a three phase power cable including the cable segment, wherein the cable electrically connects artificial lift equipment within a borehole to a surface system; one or more measurement and/or control units coupled to the cable segment by the inductive coupling device.
 10. An inductive coupling method comprising: fitting a C-shaped core around an end conductor within a flat three phase power cable segment and outside armor for the cable segment; inductively drawing power from three phase power transmitted on the cable segment with a winding around at least a portion of the C-shaped core.
 11. The method according to claim 10, further comprising: fitting an other C-shaped core around an other end conductor with the cable segment and outside the armor; and inductively drawing power from three phase power transmitted on the cable segment with a winding around at least a portion of the other C-shaped core.
 12. The method according to claim 10, further comprising: disposing a straight core proximate the cable segment, outside the armor, and oriented transverse to conductors within the cable segment; and inductively impressing or detecting signals on the cable segment with a winding around at least a portion of the straight core.
 13. An inductive coupling method comprising: disposing a straight core proximate a flat three phase power cable segment on one side of the cable segment and outside armor for the cable segment, the straight core oriented transverse to conductors within the cable segment; and inductively impressing or detecting signals on the cable segment with a winding around at least a portion of the straight core.
 14. The method according to claim 13, further comprising: disposing an other straight core proximate the cable segment on an opposite side of the cable segment and outside armor for the cable segment, the straight core oriented transverse to conductors within the cable segment; and inductively impressing or detecting signals on the cable segment with a winding around at least a portion of the other straight core.
 15. The method according to claim 13, further comprising: fitting a C-shaped core around an end conductor within the cable segment and outside armor for the cable segment; inductively drawing power from three phase power transmitted on the cable segment with a winding around at least a portion of the C-shaped core. 